A representation of a typical engine system 10 is shown in FIG. 1 in which the engine system comprises four cylinders (1, 2, 3, 4) which are coupled to a crankshaft 11. The crankshaft carries a flywheel 12 which comprises a number of teeth 14 on its outer periphery. The teeth are equally spaced about the periphery of the flywheel apart from in one or more regions 16 where there is a gap in the teeth. In FIG. 1 only one region 16 is shown but it will be appreciated that there may be, for example, two gaps in the teeth.
A crank sensor 18, for example, a variable reluctance sensor or a Hall effect sensor (used for stop/start option), is shown in proximity to the flywheel 12. The sensor is used to detect motion of the crank teeth 14 and the decoded signal output from the sensor 18 is used to provide position information which is used for engine speed measurement and fuel pulse scheduling. It is noted that any suitable sensor may be used to measure crank tooth motion, e.g. an optical based sensor may be used. It is also noted that any suitable flywheel arrangement (i.e. number of teeth and configuration of teeth) may be used to provide crank angle positions.
Each cylinder is associated with an injector (20, 22, 24, 26), the injectors in turn being in fluid communication with a common rail (not shown in FIG. 1).
A cam arrangement (comprising a camshaft 28 and a plurality of cams 30) controls the opening and closing of the air inlet 32 and outlet valves 34. A cam sensor 36 is associated with the cam shaft 28.
The crank sensor 18 and cam sensor 36 output signals to an engine control unit 38.
It is noted that in current 4-stroke internal combustion engines the fuel injection or ignition timing are controlled using these two sensors (crank sensor and cam sensor). The crank sensor essentially counts the flywheel teeth (typically a total of 60 teeth with two teeth missing. It is noted that the flywheel has two missing teeth to allow measurement of absolute crank angle position and cylinder 1 top dead centre position) in order to return engine speed data and crankshaft position and the cam sensor is arranged to generate a signal every two engine revolutions to indicate that a given cylinder is in its compression stroke and therefore ready for ignition or injection.
It is noted that the crank sensor may also be used to calculate the instantaneous rotation speed for various engine control strategies like torque cylinder balancing and injector fuelling corrections.
It is also noted that in some recent systems, the cam sensor is configured to generate more than one signal per revolution to reduce dead synchronisation time (for example many recent cam arrangements generate three targets per camshaft revolution).
FIG. 2 shows an example of a known configuration used to determine a standard injection timing angle. It is noted that in FIG. 2 the cylinders fire in the following sequence during engine operation: cylinder 2; cylinder 1; cylinder 3; cylinder 4; cylinder 2 etc.
In known engine systems conventional phasing using the output of the cam sensor means that during engine start up the system is calibrated to make its first injection on the second cylinder in the engine (referred to as second top dead centre or second TDC) in order to avoid an incomplete ignition on the first cylinder due to low cylinder gas pressure and temperature. In FIG. 2 this means that the ECU does not inject initially into cylinder 2 (which appears first in the engine block) but “skips” to cylinder 1 which is next in the sequence. The order on engine start up is therefore: cylinder 1; cylinder 3; cylinder 4; cylinder 2. This cylinder skipping has the effect of delaying engine start up.
It is an object of the present invention to overcome or substantially mitigate problems with the prior art.